Cloning and expression in Escherichia coli of the full-length and deletion variants of a human papillomavirus 18 L1 gene isolated from a Cuban patient

Abstract

Introduction: Human papillomavirus (HPV) vaccines are based on the L1 major capsid protein.
Objectives: To clone the HPV-18 L1 gene from a Cuban female HPV-18-infected patient and to express the full-length and deletion variants of the cloned HPV-18 L1 gene in Escherichia coli.
Methods: The full-length HPV-18 L1 gene was PCR-amplified from total DNA isolated from a Cuban patient, cloned and finally subcloned into the E. coli expression vector pET26b. Three deletion mutants were constructed, which encode truncated proteins lacking 30 amino acids at the C-terminus in combination with 5, 6 or none deleted residue at the N-terminus. Production of L1 proteins in E. coli BL21(DE3) and E. coli SHuffle T7 was assessed by SDS-PAGE and Western blotting.
Results: The cloned HPV-18 L1 gene was 99.9 % similar to the African variant EF202152 and probably shares a common origin with the B lineage of genotype 18. The three truncated variants of HPV-18 L1 were produced at higher levels than the full-length HPV-18 L1 protein, attaining higher levels in E. coli BL21(DE3) and higher solubility in E. coli SHuffle. The C-terminus-only truncated variant, L1∆C30, was produced at similar levels to the HPV-18 L1s truncated at both termini. E. coli SHuffle produced about three times more amounts of L1∆C30 when grown under autoinduction conditions with respect to conventional induction and thus, amounts were comparable to those obtained in E. coli BL21(DE3) under conventional induction.
Conclusions: Truncation of thirty amino acid residues at the carboxy-terminus of the HPV-18 L1 made a major contribution to the production and solubility of this wild-type protein in E. coli. This is the first report about soluble production of HPV-18 L1 protein in an E. coli SHuffle strain. However, higher amounts of L1 are needed to scale-up its production for developing an HPV vaccine candidate.